Voltage regulator for generators



July 26, 1966 F. DlETL 3,263,155

VOLTAGE REGULATOR FOR GENERATORS Filed April 1. 1963 Mum //v VE/V TORFranz D l Patented July 26, 1966 3,263,155 VOLTAGE REGULATOR FORGENERATORS Franz Dietl, Stuttgart, Germany, assignor to Robert Bosch,G.m.b.H., Stuttgart, Germany.

Filed Apr. 1, 1963, Ser. No. 269,361 Claims priority, applicationGermany, Apr. 7, 1962, B 66,709 4 Claims. (Cl. 322-28) The presentinvention concerns a voltage regulator for a self-excited generatorhaving a shunt exciter winding and being operable at greatly varyingspeeds as is particularly the case where a generator is operated on avehicle and with a speed depending upon the traveling speed or on theengine speed of the vehicle.

Essentially the present invention is an improvement of known voltagearrangements of the type set forth. In voltage regulators of this typethe ex-citer winding is connected at one of its two ends with thecollector electrode of a main transistor forming part of the regulatorand is supplied intermittent-1y or periodically with current via theemitter-collector circuit of the main transistor. In order to assureexcitation when the generator is started from standstill, the baseelectrode of the main transistor is connected with the other end of theexciter winding via a baseresistor, and for controlling the maintransistor depending upon the varying output voltage of the generator acontrol transi'stor'is provided the base electrode of which is soconnected with an output of the generator that it carries a potentialproportional to the output voltage. a .It has been foundthat knownregulator arrangements of this type are'exposed to .the danger that ashort-circuit develops within the exciter winding whereby the ohmicresistance thereof is reduced to such an extent that the main transistoris overloaded and destroyed. It has been observed that evenshort-circuits which last only through fractions of a second alreadycause a breakdown of th main transistor.

It is therefore one of the objects of this invention to electrode andserving to alternatively rendering the main transistor non-conductivewhen the output voltage of the generator is superior to a predeterminedvalue, and for provided for an improvement of conventional voltageregulators of the type set forth in such a manner that the regulatorcircuits and particularly its main transistor are protected againstoverload.

It is another object of the present invention to provide for an improvedvoltage regulator as mentioned above, the protective circuit meansthereof being so constructed that they become active immediatelyupon.the occurrence of a short-circuit as mentioned, however make itpossible that after the disappearance of the short-circuit the fulloperativeness of the regulator and therefore of .the generator isre-established.

It is still another object of the invention to provide for an improvedvoltage regulator arrangement of the type set forth which is composed ofa comparatively small number of entirely reliable and conventionalcircuit components.

With above objects in view the invention includes a voltage regulatorfor a self-exoited generator having a shunt exc-iter winding and beingoperatable at greatly varying speeds which comprises, in the firstplace, main transistor means having a collector, an emitter, and a baseelectrode, arranged for controlling the exciter current of thegenerator, the collector-emitter circuit of the transistor beingconnected in series with one of the shunt exciter winding. Forassuringexcitation upon starting of the generator from standstill a baseresistor connected between the base electrode of the main transistor andthe other end of the shunt exciter winding is provided. The regulatorarrangement further comprises control transistor means having also acollector, an emitter and a base rendering the main transistorconductive when the output voltage is inferior to that predeterminedvalue. For this purpose the base electrode of the control transistor iscon nected with one output of the generator so as to carry a potentialproportional to the output voltage thereof. For protecting thearrangement as mentioned above the arrangement finally comprisesprotective circuit means cooperating w-i-th the main and controltransistors for shortcirc-uiting said control transistor and forrendering the main transistor non-conductive when the exciter currentthrough the collector-emitter circuit of the main transistor exceeds apredetermined maximum, even when the output voltage of the generator isstill inferior .to the above mentioned predetermined value.

Preferably, the protective circuit means mentioned above comprise aseries-resistor connected at one of its ends in series with the emitterelectrode of the main transistor for producing a voltage drop dependingupon the exciter current flowing through the main transistor, and acontrollable semiconductor rectifier having a control electrode and ananode-cathode circuit, the latter being connected between a junctionpoint located between the base resistor mentioned above and the baseelectrode of the main transistor, on one hand, and the other end of theseries resistor, on the other hand, the control electrode of thesemiconductor rectifier being connected with the series-resistor forcausing the voltage drop thereacross to control the semiconductorrectifier in such a manner that the control transistor isshor-t-circuited and the main transistor is rendered non-conductive whenthe exciter current through the main transistor exceeds a predeterminedmaximum, even when the generator output'voltage is inferior to thepredetermined value thereof.

It is advisable to connect the semiconductor rectifier in parallel withthe emitter-collector circuit of the control transistor. In this case itis also advisable to choose the breakdown voltage of the controllablesemiconductor rectifier to be substantially higher than the outputvoltage of the generator to be kept at a. predetermined constant valueby means of the regulator arrangement. For instance, if the operatingvoltage of the generator is higher 'than about volts, then according toa further feature of this invention it would be advisable to connect, inseries with the anode-cathode circuit of the semiconductor rectifier, asemiconductor diode or unidirectional conductor passing the current inthe same direction as the rectifier, and to connect this diode directlywith the collector of the control transistor while additionally thejunction point between the semiconductor rectifier and the diode isconnected with the intermediate point of a voltage divider, consistingof at least two resistors in series connect-ion and connected as a wholeacross the generator so as to produce at said intermediate pointafraction of the output voltage of the generator.

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connection with the accompanying drawing, inwhich:

FIG. 1 is a diagrammatic elevational view of a lighting generatoradapted to be used on a railroad car and combined with a regulator andwith a storage battery connected in parallel with the generator;

FIG. 2 is a schematic circuit diagram of anarrangemerit according toFIG. 1, including one embodiment of a regulator arrangement according tothe invention; and

FIG. 3 is a schematic circuit diagram illustrating a modification of theregulator arrangement according to FIG. 2.

The generator of the arrangement according to FIG. 1 contains in itshousing a direct current armature (indicated at in FIG. 2) carried by anarmature shaft 12 and rotatable by means of a V-belt pulley 11, while ashunt ex-citer winding 16 is mounted inside the housing 10 and isconnected at one of its ends with the positive terminal 17 of thegenerator via the corresponding positive output line 18. A storagebattery 21 is connected at its positive terminal via a rectifier 22,conductive in the appropriate direction, with the positive output line18, while the negative terminal of the battery 22 is connected via thenegative output line with the negative terminal 19 of the generator. Ina well known manner the arrangement is such that the battery 21 can becharged and at the same timeother current consumers can be supplied withenergy when the output voltage of the generator available between thelines 18 and 20 rises above 110 volts.

In order to prevent this output voltage to increase beyond the abovementioned predetermined value when the rotary speed of the generatorshaft 12 is very considerably increased, an electronic voltage regulator25 is provided which may be mounted on the housing 10 of the generatoras shown in FIG. 1 and whose circuit arrangement is illustrated in FIG.2 within the dotted frame 25.

In particular, the voltage regulator 25 comprises a main transistor 26which has a collector electrode connected with the other end of theexciter winding 16, and additionally a control transistor 27 which hasthe function of changing the main transistor 26 from conductive tononconductive condition every time when the output voltage of thegenerator tends to exceed a predetermined value thereof. However, inorder to assure, when the generator is started from standstill, that themain transistor 26 is in conductive condition so that the generator canexcite itself, a series-combination of a base resistor 28 of, e.g., 160ohms, a resistor 29 of 40 ohms and a rectifier 30 passing current fromthe positive line 18 toward the base electrode of the main transistor 26is provided between the positive output line 18 and the base electrodeof the main transistor 26. The control transistor 27 has a collectorelectrode which is connected with the junction point between theresistors 28 and 29. Between the base electrode of the main transistor26 and the collector electrode of the control transistor 27 a capacitor31 is placed of about 0.1 ,uf. The emitter of the control transistor 27is directly connected to the negative output line 20.

Between the output lines 18 and 20 a series-combination of a resistor 33and of a potentiometer 34 is arranged. A Zener diode 35 is connectedwith one of its terminals with the movable tap 32 of the potentiometer34, while the other terminal of the Zener diode 35 is connected with thebase electrode of the control transistor 27 and additionally with oneend of a resistor 36 of about 200 ohms, the other end whereof isconnected with the negative output line 20. The breakdown voltage of theZener diode is so chosen that the latter becomes conductive when theoutput voltage of the generator as available between the two outputlines 18 and 20 exceeds the predetermined value of, e.g., 110 volts.When this occurs a control current can flow from the tap 32 via theZener diode to the base electrode of the control transistor 27 and fromthere through the emitter to the negative output line 20, this currentrendering the emitter-collector circuit of the control transistor 27conductive whereby the main transistor 26 is rendered non-conductive aswill be described further below.

As long as the predetermined value of the output voltage is not reachedthe control transistor 27 remains in non-conductive condition andconsequently the main transistor 26 is fully conductive. When this isthe case the base current of the main transistor 26 flowing through theresistor 29 produces across the latter a voltage drop of about 20 volts.Under this condition that electrode of the capacitor 31 which isconnected with the collector of the control transistor 27 is charged toa voltage differing from that of the other electrode of the capacitor 31which is connected with the base electrode of the main transistor 26.When now the output voltage of the generator exceeds the predeterminedvalue of, e.g., 110 volts the control transistor together with the Zenerdiode 35 becomes conductive. The collector current of the controltransistor 27, flowing through the base resistor 28 produces across thelatter a voltage drop of about volts to which is now added the existingcharge of the capacitor 31 whereby the potential at the base of the maintransistor 26 is reduced to a value which is about 10 volts lower thanthe potential of the negative output line 20. Hereby the main transistor26 is rendered completely non-conductive and the exciter current whichup to this moment could flow through the exciter winding 16 isinterrupted. The inductive voltage peak generated at the moment of thecurrent interruption is substantially taken care of and diverted by arectifier 37 which is conductive in the proper direction and connectsthe collector of the main transistor 26 with the positive output line18. The remainder of the inductive voltage peak is applied via aresistor 38 and a series-connected capacitor 39 in such a manner to thebase electrode of the control transistor 27 that the latter is kept inconductive condition through a period of time which is determined by thecharging time constant of the capacitor 39.

Due to the now lacking exciter current the output voltage of thegenerator drops rapidly below the above mentioned predetermined valuethereof. As a result, the control current for the transistor 27 which upto this moment was flowing through the Zener diode 35 cannot bemaintained any longer so that the control transistor 2 27 now returns toits non-conductive condition. Consequently, the main transistor 26 isnow able to return to its original conductive condition and will carryan exciter current flowing through the exciter winding 16 until theoutput voltage again reaches the predetermined value thereof whereafterthe cycle repeats.

In order now to protect the main transistor 26 against the danger thatin the case of a short-circuit occurring in the field winding 16 thefull amount or at least a substantial portion of the voltage existingbetween the output lines 18 and 20 has to be carried by theemittercollector circuit of the main transistor 26, the inventionprovides a protective arrangement as follows. The protective arrangementaccording to the invention comprises a series resistor 40 connectedbetween the main transistor 26 and the negative output line 20, andpreferably a potentiometer 41 connected in parallel with the seriesresistor 40. Moreover a controllable semiconductor rectifier 42 isprovided the anode whereof is connected with the collector of thecontrol transistor 27 while its cathode is directly connected with thenegative output line 20. The semiconductor rectifier has a controlelectrode 43 which is connected with the movable tap 44 of thepotentiometer 41 so that, depending upon the setting of the tap 44, thesemiconductor rectifier is rendered conductive as soon as a voltage dropof more than 10 volts appears between the emitter electrode of the maintransistor 26 and the negative output line 20. This will occur when theemitter current of the main transistor 26 exceeds a maximum permissiblevalue of, e.g., 1.5 amperes. When the semiconductor rectifier 42 isrendered conductive then it constitutes a low resistance short-circuitfor the control transistor 27 and carries a current flowing through thebase resistor 28 and having so large an amplitude that the maintransistor 26 is returned to its nonconductive condition even when theoutput voltage of the generator should have dropped already below theabove mentioned predetermined value thereof. Only when the excitation ofthe generator has almost entirely vanished and when its output voltagehas droped to a very low value, the semiconductor rectifier 42automatically returns to its non-conductive condition. In case that theshort-circuit in the exciter winding hasbeen eliminated or has vanishedin the meantime, then the excitation of the generator will start againand the regulator arrangement will operate in the manner describedfurther above. However, should upon the new excitation of the generatorthe short-circuit still exists and apply to a great portion of theexciter winding, then the generator cannot be excited again. On theother hand, if the shortcircuit applies only to a very small portion ofthe exciter winding 16 then the generator will be able to excite itselfagain. In any case however, as soon as the above mentioned criticalvalue of 1.5 amperes of the exciter current flowing through the seriesresistor 40 is reached the semiconductor rectifier 42 is again renderedconductive and causes in the above described manner non-conductivecondition of the main transistor 26.

e FIG. 3 illustrates only theregulator portion of a generatorarrangement as described above. The modified regulator arrangement shownwithin the dotted frame 50 may be used in the same manner as theregulator arrangement according to FIG. 2 in the lighting installationof a vehicle. FIG. 3 contains elements identical or equivalent to thoseof the arrangement according toFIG. 2, the same reference'numerals havebeen used in the drawing. The main difference between the arrangementsof FIGS. 2 and 3 consists in the provision of a plain not controllablerectifier or diode or unidirectional conductor 53 in series with thecontrollable semiconductor rectifier 52, both connected as aseries-combination in the connection between the collector of thecontrol transistor 27 and the negative output line 20. The rectifier ordiode 53 is connected with its anode directly with the collector of thecontrol transistor 27. Since the controllable rectifier 52 can carryonly a comparatively low breakdown voltage between its anode and itscathode which is connected with the nega tive output line 20, and inorder to make it possible to utilize the rectifier 52 also in aregulator arrangement operating with comparatively high voltages, avoltage divider comprising at least two resistors 54 and 55 is arrangedbetween the positive output line 18 and the negative output line 20. Theintermediate point A of the voltage divider, located between theresistors 54 and 55 is connected with the anode of the controllablerectifier 52 as Well as with the cathode of the series-connected.noncontrollable rectifier 53. The control electrode of the rectifier 52is connected as in the previous example with the movable tap 44 of thepotentiometer 41 which is again connected in parallel with the seriesresistor arranged in the emitter connection of the main transistor 26.The voltage divider resistors 54 and 55 are so dimensioned that thepotential at the intermediate point A is always higher than thepotential of the collector of the control transistor 27.

In this arrangement the controllable rectifier 52 remains innon-conductive condition until the exciter current flowing through theseries resistor reaches a maximum permissible value which ispredetermined by the setting of the movable tap 44. Whenever this occursthe controllable rectifier 52 by becoming conductive constitutes ashort-circut for the resistor 55 and consequently causes the collectorof the control transistor 27 to assume a potential which issubstantially equal to that of the negative output line 20 because underthis condition the rectifier 53 constitutes only a low resistanceconnection to the controllable rectifier 52 which is also in highlyconductive condition.

The not'controllable rectifier 53 has the additional As far as thearrangement according to function to prevent during lator the voltageavailable at the intermediate point A between the voltage dividerresistors 54 and 55 from influencing the base electrode of the maintransistor 26. In this manner it is assured that the main transistor 26is sufiiciently rendered non-conductive when the control transistor 27assumes conductive condition at the moment when the output voltage ofthe generator exceeds its predetermined value.

A particular advantage of the above described protective arrangementaccording to the invention resides in the following facts: Whenever thecontrollable rectifiers 42 or 52 are rendered conductive on account of ashortcircuit occurring in the field or exciter winding, the controllablerectifier remains in this condition even in the absence of a controlvoltage at its control electrode 43 as long as a voltage differenceexists between the output lines 18 and 20 of the generator. Even if theshortcircuit is immediately eliminated, the excitation of the generatormust first disappear almost completely and the voltage of the generatormust drop to a value amounting almost to zero, before the rectifierassumes non-conductive condition and thereby again renders the maintransistor 26 conductive. In this manner -it is assured that the maintransistor cannot be overloaded. As a matter of fact, this would sooncause a breakdown between its collector and its emitter whereby thiscollector-emitter circuit would be rendered permanently conductive. Ifthis should occur in the presence of a short-circuit concerning only aportion of the exciter winding 16, this would entail a great increase ofthe generator output voltage and result no only in a rapid destructionof the control transistor 27 and of the Zener diode 35, but also of thestorage battery 21 and the generator itself.

It will be understood that each of the elements described above, or-twoor more together, may also find a useful application in other types ofvoltage, regulator for a self-excited generator differing from the typesdescribed above.

- While the invention has been illustrated and described as embodied involtage regulator for a self-excited gene-rator having a shuntexciter'winding and being operatable at greatly varying speeds, it isnot intended to be limited to the details shown, sincevarious-modifications and structherefore, such adaptations should andare intended-to be comprehended within the meaning and range ofequivalence of the following claims. I

- What is claimed as new and desired to be secured by Letters Patent is:

. 1. Voltage regulator for a self-excited generator having a shuntexciter winding and'being operable at greatly varying speeds,comprising, in combination, main transistor means having collector,emitter and base electrodes, -respectively, for controlling the excitercurrent of the generator, the collector-emitter circuit of saidtransistor means being connected in series with one end of the shuntexciter winding; base resistor means connected between said baseelectrode and the other end of said shun-t exciter winding for assuringexcitation upon starting the generator from standstill, controltransistor means having collector,-

emitter and base electrodes, respectively, for alternatively renderingsaid main transistor means non-conductive when the output ofvoltage ofthe generator is superior to a predetermined value, and for renderingsaid main transistor means conductive when said output voltage isinferior to said predetermined value, said collector electrode of saidcontrol transistor means being connected both with a normal operation ofthe regujunction point between said base resistor means and said baseelectrode of said main transistor means, said base electrode of saidcontrol transistor means being connected with one output of thegenerator so as to carry a potential proportional to said outputvoltage; series-resistor means connected .at one of its ends in serieswith said emitter electrode of said main transistor means for producinga voltage drop depending upon said exciter current flowing through saidmain transistor means; and controllable semiconductor rectifier meanshaving a control electrode and an anode-cathode circuit, the latterbeing connected between a junction point located between said baseresistor means and said base electrode of said main transistor means, onone hand, and the other end of said series resistor means, on the otherhand, said control electrode of said semiconductor rectifier means beingconnected with said series-resistor means for causing said voltage dropthereacross to control said semiconductor rectifier means, in such amanner that said control transisitor means is short-circuited and saidmain transistor means is rendered non-conductive when said excitercurrent through said main transistor means exceeds a predeterminedmaximum, even when the generator output voltage is inferior to saidpredetermined value thereof.

2. Voltage regulator for a self-excited generator having a shunt exciterwinding and being operable at greatly varying speeds, comprising, incombination, main transistor means having collector, emitter and baseelectrodes, respectively, for controlling the exciter current of thegenerator, the collector-emitter circuit of said transistor means beingconnected in series with one end of the shunt exciter winding; baseresistor means connected between said base electrode and the other endof said shunt exciter winding for assuring excitation upon starting thegenerator from standstill, control transistor means having collector,emitter and base electrodes, respectively, for alternatively renderingsaid main transistor means nonconductive when the output voltage of thegenerator is superior to a predetermined value, and for rendering saidmain transistor means conductive when said output voltage is inferior tosaid predetermined value, said collector electrode of said controltransistor means being connected both with a junction point between saidbase resistor means and said base electrode of said main transistormeans, said base electrode of said control transistor means beingconnected with one output of the generator so as to carry a potentialproportional to said output voltage; series-resistor means connected atone of its ends in series with said emitter electrode of said maintransistor means for producing a voltage drop depending upon saidexciter current flowing through said main transistor means; voltagedivider means connected across the generator for furnishing at apredetermined intermediate point a reference voltage being apredetermined fraction of the generator output voltage; and aseries-combination of a unidirectional conductor means and of acontrollable semiconductor rectifier means having a control electrodeand an anode-cathode circuit, said series-combination being connectedbetween a junction point located between said base resistor means andsaid base electrode of said transistor means, on one hand, and the otherend of said series resistor means, on the other hand, the junction pointbetween said unidirectional coduct-or means and said semiconductorrectifier means being connected with said intermediate point of saidvoltage divider means, and said control electrode of said semiconductorrectifier means being connected with said series-resistor means forcausing said voltage drop thereacross to control said semiconductorrectifier means, in such a manner that said control transistor means isshort-circuited and said main transistor means is renderednon-conductive when said exciter current through said main transistormeans exceeds a predetermined maximum, even when the generator outputvoltage is inferior to said predetermined value thereof.

3. Voltage regulator for a self-excited generator having (3 0 a shuntexciter winding and being operable at greatly varying speeds,comprising, in combination, main transistor means having collector,emitter ad base electrodes, respectively, for controlling the excitercurrent of the generator, the collector-emitter circuit ofsaid'transistor means being connected in series with one end of theshunt exciter Winding; base resistor means connected between said baseelectrode andthe other end of said shunt exciter winding for assuringexcitation upon starting the generator from standstill, controltransistor means having collector, emitter and base electrodes,respectively, for alternatively rendering said main transistor meansnon-conductive when the output voltage of the generator is superior to apredetermined value, and for rendering said main transistor meansconductive when said output voltage is inferior to said predeterminedvalue, said collector electrode of said control transistor means beingconnected both with a junction point between said base resistor meansand said base electrode of said main transistor means, said baseelectrode of said control transistor means being connected with oneoutput of the generator so as to carry a potential proportional to saidoutput voltage; seriesresistor means connected at one of its ends inseries with said emitter electrode of said main transistor means forproducing a voltage drop depending upon said exciter current flowingthrough said main transistor means; and contr-ollable semiconductorrectifier means having a control electrode and an anode-cathode circuit,the latter being connected between a junction point located between saidbase resistor means and said base electrode of said main transistormeans, on one hand, and the other end of said series resistor means, onthe other hand, potentiometer means being connected in parallel withsaid series-resistor means, and said control electrode of saidsemiconductor rectifier means being connected with an intermediatetapping point of said potentiometer means for causing a predeterminedfraction of said voltage drop across said seriesresistor means asavailable atsaid tapping point to control said semiconductor rectifiermeans, in such a manner that said control transistor means isshort-circuited and said main transistor means is renderednon-conductive when said exciter current through said main transistormeans exceeds a predetermined maximum, even when the generator outputvoltage is inferior to said predetermined value thereof.

4. Voltage regulator for a self-excited generator having a shunt exciterwinding and being operable at greatly varying speeds, comprising, incombination, main transistor means having collector, emitter and baseelectrodes, respectively, for controlling the exciter current of thegenerator, the collector-emitter circuit of said transistor means beingconnected in series with one end of the shunt exciter Winding; baseresistor means connected between said base electrode and the other endof said shunt exciter winding for assuring excitation upon starting thegenerator from standstill, control transistor means having collector,emitter and base electrodes, respectively, for alternatively renderingsaid main transistor means non-conductive when the output voltage of thegenerator is superior to a predetermined value, and for rendering saidmain transistor means conductive when said output voltage is inferior tosaid predetermined value, said collector electrode of said controltransistor means being connected both with a junction point between saidbase resistor means and said base electrode of said main transistormeans, said base electrode of said control transistor means beingconnected with one output of the generator so as to carry a potentialproportional to said output voltage; series-resistor means connected atone of its ends in series with said emitter electrode of said maintransistor means for producing a voltage drop depending upon saidexciter current flowing through said main transistor means; voltagedivider means connected across the generator for furnishing at apredetermined intermediate point a reference voltage being apredetermined fraction of the generator output voltage;

9 and a series-combination of a unidirectional conductor means and of acontrollable semiconductor rectifier means having a control electrodeand an anode-cathode circuit, said series-combination being connectedbetween a junction point located between said base resistor means andsaid base electrode of said transistor means, on one hand, and the otherend of said series resistor means, on the other hand, the junction pointbetween said unidirectional conductor means and said semiconductorrectifier means being connected with said intermediate point of saidvoltage divider means, potentiometer means being connected in parallelwith said series-resistor means, said control electrode of saidsemiconductor rectifier means being connected with an intermediatetapping point of said potentiometer means for causing a predeterminedfraction of said voltage drop across said series-resistor means asavailable at said tapping point'to control said semiconductor rectifiermeans, in such a manner that said control transistor means isshort-circuited and said main transistor means is renderednon-conductive when said exciter current through said main transistormeans exceeds a predetermined maximum, even when the generator outputvoltage is inferior to said predetermined value thereof.

References Cited by the Examiner UNITED STATES PATENTS 3,098,964 7/ 1963Hetzler 322-28 3,179,874 4/ 1965 Guennou 32225 3,193,755 7/1965 Zelina322-28 3,201,681 8/1965 Van Wilgen et a1. 322-25 X MILTON O. HIRSHFIELD,Primary Examiner. J. J. SWARTZ, Assistant Examiner.

1. VOLTAGE REGULATOR FOR A SELF-EXCITED GENERATOR HAVING A SHUNT EXCITERWINDING AND BEING OPERABLE AT GREATELY VARYING SPEEDS, COMPRISING, INCOMBINATION, MAIN TRANSISTOR MEANS HAVING COLLECTOR, EMITTER AND BASEELECTRODES, RESPECTIVELY, FOR CONTROLLING THE EXCITER CURRENT OF THEGENERATOR, THE COLLECTOR-EMITTER CIRCUIT OF SAID TRANSISTOR MEANS BEINGCONNECTED IN SERIES WITH ONE END OF THE SHUNT EXCITER WINDING; BASERESISTOR MEANS CONNECTED BETWEEN SAID BASE ELECTRODE AND THE OTHER ENDOF SAID SHUNT EXCITER WINDING FOR ASSURING EXCITATION UPON STARTING THEGENERATOR FROM STANDSTILL, CONTROL TRANSISTOR MEANS HAVING COLLECTOR,EMITTER AND BASE ELECTRODES, RESPECTIVELY, FOR ALTERNATIVELY RENDERINGSAID MAIN TRANSISTOR MEANS NON-CONDUCTIVE WHEN THE OUTPUT OF VOLTAGE OFTHE GENERATOR IS SUPERIOR TO A PREDETERMINED VALUE, AND FOR RENDERINGSAID MAIN TRANSISTOR MEANS CONDUCTIVE WHEN SAID OUTPUT VOLTAGE ISINFERIOR TO SAID PREDETERMINED VALUE, SAID COLLECTOR ELECTRODE OF SAIDCONTROL TRANSISTOR MEANS BEING CONNECTED BOTH WITH A JUNCTION POINTBETWEEN SAID BASE RESISTOR MEANS AND SAID BASE ELECTRODE OF SAID MAINTRANSISTOR MEANS, SAID BASE ELECTRODE OF SAID CONTROL TRANSISTOR MEANSBEING CONNECTED WITH ONE OUTPUT OF THE GENERATOR SO AS TO CARRY APOTENTIAL PROPORTIONAL TO SAID OUTPUT VOLTAGE: SERIES-RESISTOR MEANS